1. Field of the Invention
The present invention relates to compression of color codes for pixels in raster images, and involves compression of selected ones of the pixels by using adjacent pixels and predetermined colors.
2. Description of the Related Art
As resolution of computerized color images increases, the amount of storage needed to store such images has increased dramatically. For example, for computerized images at 400 dots per inch (dpi) resolution, each square inch of image area is formed by a 400.times.400 pixel matrix. Consequently, for a standard 81/2.times.11 inch page, information for 14,960,000 pixels needs to be stored. For a four color image (such as cyan, magenta, yellow and black colors), at eight bits per color, 57 megabytes of memory are needed.
Such memory requirements strain even the most advanced personal computing equipment available today. Typically, for example, it will be expected that a user will view, manipulate, change and otherwise process the image prior to storage or viewing or printing. To do so, the image must be stored in active memory which, for the above-mentioned 81/2 .times.11 inch image, would need to be at least 57 megabytes. In addition, the time required simply to transfer an image of this size, i.e., from disk memory across a computer bus to active memory or to a printer, is enormous.
In view of the storage requirements for modern, high resolution pixel images, various compression techniques have been proposed so as to compress the image to a size that is more manageable. These compression techniques include lossy compression techniques, such as JPEG compression, sub-sampling, pixel quantization and the like, and also include non-lossy techniques such as run length encoding. These known compression techniques all have drawbacks, such as uncertain compression ratios and a slow speed for implementation, which render them useless for on-the-fly real-time usage by a computer user during image processing. Accordingly, while these known compression techniques are similar to the present invention in that their object is to compress images, they are quite different in structure and operation from the present invention.